1. Field of the Invention
The present invention relates generally to optical communications. Specifically, this invention relates to controlling the variation of optical fiber amplifier gain due to changes in temperature.
2. Description of the Related Art
Optical fiber communications systems provide for low loss and very high information carrying capacity. Most advanced optical fiber communication systems now in place owe success and operating characteristics to optical fiber amplifiers such as the erbium-doped fiber amplifier (EDFA). The gain bandwidth of this amplifier is sufficient to permit simultaneous amplification of multiple channels and, for this reason may be used for dense wavelength division multiplexing (DVVDM).
In optical fiber amplifiers, like EDFAs, for DWDM systems the gain spectrum is required to be approximately uniform. However, as the temperature of the optical fiber varies, the shape of the gain spectrum changes significantly. It would be useful to control this variation of gain or to compensate within the amplifier for the variation.
Several solutions have been proposed or attempted. One of the attempted solutions deals with controlling the temperature of the optical fiber with a heater. This solution though causes high heat in the optical fiber which reduces the overall life and reliability of the optical fiber.
Another proposed solution involves gain flattening filters which have a transmission spectrum that varies with temperature in an appropriate manner related to the gain spectrum. However, this option has not been shown to be commercially viable.